4. Intro to Vascular System

Introduction to Vascular System

• Instructor: Dr. Declan McKernan

• Email: declan.mckernan@universityofgalway.ie

• Course: PM309 Cardiovascular Drugs

Learning Outcomes

• Understand variability of blood pressure with location and cardiac cycle stages.

• Identify regulation mechanisms of blood pressure, including systems and hormones involved.

Blood Pressure Mechanics

• Dependence on two key valves:

  • Atrioventricular (AV) Valves

    • Open/close based on pressure differences between atria and ventricles.

    • Open when atrial pressure > ventricular pressure during relaxation.

  • Semilunar Valves

    • Open during systole when ventricular pressure exceeds arterial pressure.

    • Close during diastole to prevent reflux, ensuring unidirectional blood flow.

• Cardiac Cycle Phases:

  • Systole:

    • Pressure rises in ventricles causing blood ejection.

  • Diastole:

    • Ventricles fill with blood as atria contract.

Cardiac Cycle Pressure Changes

• Stages:

  • Isovolumic Relaxation: All valves closed, pressure decreases.

  • Atrial Systole: Atria contract, blood flows into ventricles.

  • Ventricular Systole: Ventricles contract, pumping blood into aorta and pulmonary artery.

Systemic Blood Pressure Regulation

Anatomy Overview

• Major Structures:

  • Aorta, vena cava, pulmonary arteries and veins, hepatic and renal arteries and veins.

• Blood Vessels Classification:

  • Elastic Arteries

  • Muscular Arteries

  • Arterioles and Capillaries

  • Venules and Veins

Blood Pressure Measurement

• Technique: Auscultation using a sphygmomanometer.

• Procedure: Inflate cuff on the brachial artery, measure

  • Systolic Pressure: First Korotkoff sound.

  • Diastolic Pressure: Last Korotkoff sound.

• Normal Values:

  • Systolic: 120 mmHg, Diastolic: 80 mmHg, Mean arterial pressure: ~90 mmHg.

Regulation of Blood Pressure

• Formula: BP = Cardiac Output (CO) x Total Peripheral Resistance.

• Cardiac Output Calculation: CO = Heart Rate (HR) x Stroke Volume (SV).

• Peripheral Resistance:

  • Depends on arteriole diameter.

  • Increased contraction leads to increased resistance.

Adrenergic Regulation

• Role of norepinephrine and adrenergic receptors in regulating vascular smooth muscle responses.

• Receptors:

  • Alpha-1: Causes contraction of vascular smooth muscle.

  • Beta-1: Increases heart rate and myocardial contractility.

  • Beta-2: Induces relaxation in smooth muscles.

Baroreceptor Reflex

• Vagal nerves decrease heart rate via K+ channel opening.

• Sympathetic system increases heart rate through norepinephrine secretion at β1 receptors.

• Baroreceptors located in carotid sinus and aortic arch sense blood pressure changes.

Renin-Angiotensin-Aldosterone System (RAAS)

• Renin Functions:

  • Enzyme released during volume depletion signals Na+/water retention, leading to vasoconstriction.

• Steps of RAAS:

  • Renin cleaves angiotensinogen to angiotensin I, which converts to angiotensin II, causing vasoconstriction and aldosterone release.

Endocrine Regulation

• Antidiuretic Hormone (ADH): Released from posterior pituitary; increases water retention and vasoconstriction.

• Endothelium-derived mediators: Include nitric oxide (NO) and prostaglandins (PGs) that affect vascular smooth muscle tone.

Summary

• Blood pressure is influenced by location, heart cycles, and is regulated systemically and locally by various factors, ensuring homeostasis.